218 PERMIAN FOSSILS. 



The reader is referred to M. Deshayes's Monograph of Dentalium, and to a paper 

 by Mr. W. Clark,^ for an account of the mollusk of this genus. 



Dentalium Sorbii, Kinff. 



Diagnosis. — Smooth ; curved ; gradually tapering. 



The above is a provisional description of a species supposed to be of the present 

 genus. It was discovered by Mr. Henry Clifton Sorby, F.G.S., who has only succeeded 

 in finding a single specimen, which is not quite perfect at the small end. The specimen 

 appears to have been about five eighths of an inch in length ; and its curvature is about 

 the same as a circle, the radius of which is from half to five eighths of an inch. 



Dentalium Sorbii occurs at Connigsborough, near Doncaster. 



Class Cephalopoda, Cuvier, 1T98. 



Cephalophora, Blainville, 



Diagnosis. — "A class of molluscous invertebrate animals, in which the head is 

 situated between the trunk and the feet, or principal organs of locomotion." (Owen.*) 



"The Cephalopods have been divided into two sections, depending on their having 

 two, or four gills ': those with two gills are termed Dibranchians, and such as have four, 

 are called Tetrabranchians. The Calamary, Cuttle-fish, Argonaut, and Spirula are 

 examples of the dibranchiate, and the Pearly Nautilus represents the tetrabranchiate 

 section."^ The latter is the only division known as having representatives in the 

 Permian system. 



Order Tetrabranchiata, Owen. 



This group contains at least two families, Nautilidce and Ammonitida, both con- 

 sisting of chambered shells ; but the former has the septa or partitions, separating 

 the chambers, generally plain at the margins, and perforated centrally or sub-marginally ; 

 whereas the latter has the plates variously lobed at the margins, and perforated 

 marginally at the medio-dorsal line of the shell. 



Family Nautilid^ {Nauiilles, restricted)^ Cuvier. 

 i)M^«os/5.— "Shell external, spiral, or straight; septa smooth and simple; the last 



1 Annals and Magazine of Natural History, 2d series, vol. iv, p. 321. 

 ' Cyclopaedia of Anatomy, vol. i, p. 517. 



3 Vide the author's paper entitled "An attempt to classify the Tetrabranchiate Cephalopods," in the 

 Ann. and Mag. of Nat. Hist.,' vol. xiv, p. 272. 



